Manufacture and processing of discharge devices



MANUFACTURE Ak iD PROCESSING OF DISCl -IARGE DEVICES Filed June 8, 19432 Sheets-Sheet 1 izlwzzzz E. B. NOEL 2,353,783 MANUFACTURE ANDPROCESSING OF DISCHARGE DEVICES July 18, 1944.

Filed June 8, 1943 2 Sheets-Sheet 2 I I I H H His At'irovneg PatentedJuly 18, 1944.

MANUFACTURE AND PROCESSING OF DISCHARGE DEVICES Edward B. Noel, Clevelanor to General Electric of New York d Heights, Ohio, assim- Company, acorporation Application June 8, 1943, Serial No. 490,061 2 Claims. (Cl.316-18) This invention relates to the manuf cture and processing ofvitreous or refractory-walled devices, such as electric dischargedevices or lamps useful as sources of radiation for various purposes.The invention is especially useful in connection with devices thatconvert considerable energy to light or other desired radiation in verysmall space, and therefore usually operate witlr relatively highinternal pressures and temperatu1'essuch, for example, as the smalltubular or capillary lamps marketed under the designations H-3, H-6, andAH-lO, as well as certain high-pressure lamps having small sphericaldischarge envelopes, usually with tubular extensions or "end chambersaround their electrode leads. In some cases, the amount of energyunavoidably dissipated as heat in such devices is so great that forcibleexternal cooling by water or air is necessary, to prevent fusion ordevitrification of their envelopes. Fused quartz or quartz glass isabout the most refractory light and radiationtransmitting materialpractically available, and is generally employed for the envelopes oflamps of this kind, though in some cases hard glass less refractory thanquartz may be used, when the operating temperatures are not too high.

In the manufacture of lamps of this character, the usual envelope blankmay be a vitreous tube, or a spherical vitreous bulb with opposedtubular extensions or ends. Sometimes a spherical bulb having a singletubular end or neck may be used, both inleads to the electrodes beingintroduced through this neck. In any case, the electrodes are mountedopposite or adjacent one another in the midst of the tube or bulb, whichprovides the discharge space of the completed lamp, and are attached tothe inner ends of current leads which are sealed into the envelopeend(s) or neck by fusing and collapsing the latter around the leads.Owing to the high softening points of vitreous materials that can standhigh operating temperatures, a correspondingly high heat is necessaryfor this sealing-in operation, with consequent danger of oxidizing thecurrent leads or the electrodes, which are usually of refractory butoxidizable metal like molybdenum or tungsten. During the process ofmanufacture, the discharge chamber for the electrodes, which is boundedby the end seal(s) around the leads, is evacuated and otherwiseconditioned for operation of the device, this exhaust processing orconditioning including introduction of any desired working substance(s).For small discharge lamps of high-pressure type, the main workingsubstance i usually mercury or other vaporizable and ionizable metalthat provides a suitable discharge atmosphere during operation, togetherwith a starting atmosphere of argon or other similar inert rare gas.After introduction of the working substance s), the device is finallyand permanently sealed off. A

It is with the manufacture and exhaust processing of these devices asabove outlined, but in a specially advantageous way, that my presentinvention is concerned. Various features and advantages of the inventionwill be better understood from the following description of species andforms of embodiment or modes of practice, and from the drawings. Theinvention is here illustrated and explained in connection with a smalltubular lamp intended to operate at moderate internal pressure with lowpressure air blast cooling-which is more fully described and claimed inapplication Serial No. 460,913 of Donald D. Hinman, filed October 5,1942, and assigned to the assignee of this application-but it will beunderstood that the invention is also applicable to lamps and dischargedevices of other typ In the drawings, Fig. 1 is an enlarged longitudinalsectional view of a quartz tubular or capillary lamp made and processedaccording to my invention, with a wiring diagram of itable electriccircuit connections, also. showing a cooling air jet nozzle pipe; Fig. 2is a side view of an envelope blank suitable for the fabrication of thelamp, with the inlead and electrode assemblies in place but not yetsealed in, the scale being smaller than for Fig. 1; Fig. 3 is a verticalsectional view of apparatus for processing the lamp, with a portion ofone part broken out, the section being taken as indicated by the lineand arrows 3-3 in Fig. 4; and Fig. 4 is a side view of the apparatus atright angles to Fig. 3, on a larger scale, also showing one part with aportion thereof broken out.

As shown in Fig. 1, the discharge device is a lamp L comprising avitreous elongated or tubular envelope ID of fused quartz (which ispermeable to ultraviolet and visible radiation) having a substantiallycylindrical form, except at its end chambers II, II, as the end portionsof the discharge space where its walls are not directly heated by thearc discharge are commonly called in this art-even when (as here shown)they are not structurally distinguished in any way from the spacethrough which the are actually ex- "tends.

At the opposite envelope ends II, II are shown solid operatingelectrodes I2, I 2 attached to the inner ends of axial inleads l3, l3which normal operating temperature.

are sealed through vitreous external cylindrical end seal extensions I4,I, shown as of a size approximating the external envelope diameter.

' The electrodes I2, I2 may be of unactivated refractory metal such astungsten. A charge of vaporizable and ionizable working substance, suchas mercury, is indicated by a droplet I5 inside the envelope III. Theenvelope II! should also contain an atmosphere of starting gas such asone of the rare'gases like argon, krypton, xenon, etc., at a moderatelylow pressure of some 20 to 100 mm., for example, argon at about 20 mm.pressure being at present preferred. The proportions and volume of thedischarge space or cavity in the envelope III represent a constrictionof the envelope such as to result in a dischargeconstrlcting pressuretherein during normal operation, and the amount of mercury I5 may besuch as to give an unsaturated mercury atmosphere of some 5 toatmospheres pressure at The cavity of the envelope III should be withoutsharp corners or any irregularities sufficient to form recesses whererelatively ineffective heating from the arc stream might allow mercuryto condense. Accordingly, the angular hollow corners that would exist atthe ends of the envelope ID if they'were flat are filled out and roundedaway. The electrodes l2, I2 are coaxial with the tube bore andapproximately cover these rounded apices of the end surfaces, with theirinner ends about in the planes where the rounded end chambers merge withthe cylindrical tube bore. They are mounted close up against theenvelope ends II, I I, almost touching the end walls, and are of suchcompact, squat proportions that they project relatively little into theend chambers of the envelope. As shown, each of the electrodes I2, I2 isconstructed out of a helical coil of a few turns of tungsten wire,comparable in gauge to the inlead wire and wound with its ownconvolutions in lateral contact, fitted around an inner inlead sectionI! of tungsten wire and preferably welded thereto.

It is preferred to make the lamp envelope entirely of one refractoryvitreous material, such as quartz, without the employment of speciallower-melting material at the end seals I4, I4. While quartz end sealsaround circular tungsten inlead wires have not provedsatisfactory-showing objectionable leakage-this can be overcome by usingribbon type end seals such as shown in Patent 2,094,694 to B01. As shownin Fig. 1, each seal I4 may comprise a length of molybdenum ribbon I8whose ends are laterally welded to inner and outer lead wire sections I1and I9, the former of tungsten and carrying an electrode l2, the latterof tungsten or molybdenum. In Fig. 1, the ribbons I8, I8 of the twoseals I4, I4 are shown as lying in planes at right angles to oneanother, though this is not at all essential. To obviate any diflicultyin welding the wires I'I, I9 to extremely thin ribbon I8 without eithermelting the latter or failing to produce joints of adequateconductivity, it is desirable to reinforce or thicken the ends of theribbon I8, which may be done by solidly welding on refractory sheetmetal facings 20, preferably at both sides of the ribbon I8. As shown inFig. 1, a short length of molybdenum ribbon, preferably thicker than theribbon I8, may be folded around each end of the latter to provide its'two facings 20, 20. After these facings 20, 20 have been welded on moreor less solidly-or at least at numerous points over charge gap of 18 mm.

the width and area of contact-the resulting virtually integral thickenedends of the ribbon I! can be laterally welded firmly and solidly to thelead wires I'I, I9 without difficulty. The final result is a lead andelectrode assembly E such as shown in Fig. l.

Cooling air from any suitable supply may be blown against one side ofthe lamp envelope II) at its mid-length through a nozzle pipe P locatedin close proximity to the envelope and supplied by. a blower (notshown), or by any suitable means. For a lamp having a discharge cavity22 mm. long and 3.5 mm. in diameter, having a disbetween the proximatetips of the electrodes I2, I2, taking about 400 watts with a dischargecurrent of about 3.6 amperes, and containing a charge I5 of 1.8 mg. ofmercury to give an unsaturated mercury atmosphere of some 5 to 10atmospheres pressure in operation, the nozzle pipe P may be of a:lnchbore and located about 1 cm. from the axis of the envelope I0, withwhich the nozzle is axially aligned. An air flow of 2 cubic ft. perminute is satisfactory, and requires an air pressure of about 1 /2 lbs.per square inch (above atmospheric) directly behind the nozzle opening.

In fabricating the lamp, a quartz envelope or bulb such as shown in Fig.2 may be made, consisting of a main tubular portion correspondingessentially to the envelope I0 as shown in Fig. 1, with integral long,heavy-walled, ends T, T, just large enough to freely pass the lead andelectrode assemblies, E, E, and with a lateral exhaust tube t openinginto the envelope I0, but preferably narrowly constricted right adjacentthe envelope as shown at 2|. The electrode assemblies E, E are placed inthe tube ends T, T. and the tube end extremities are sealed up by fusionas indicated in clot and dash lines in Fig. 2. During the sealing up ofeach tube end T. both the electrode assemblies E, E may be shifted intothe other tube end T to prevent their being overheated and damaged;afterward thew may be separated and shifted outward as far a:

- possible into the opposite tube ends T, T. Thereupon the device L maybe held horizontal and evacuated through the tube it, being preferablyheated or baked in an oven (such as hereinafter described) to atemperature of some 1200 C. to degas the internal tube walls and theelectrode assemblies E, E as much as possible. Matter expelled from theelectrode assemblies E, E during this oven baking deposits on theinternal walls of the tubular ends T, T, while the mid-portion In of thedevice (that afterward forms its discharge chamber) remains clean andunobscured. To facilitate subsequent steps (to be presently described),the exhaust tube 15 is now preferably sealed off at some distance fromthe envelope Ir-as suggested at 22 in Fig. 3thus detaching the wholedevice L from the exhaust system S and leaving it free for convenientmanipulation.

The oxidizing atmosphere being thus substantially removed and excludedfrom the interior of the envelope or device L, the electrode assembliesE, E are shifted inward toward one another to bring the electrodes I2,I2 to their proper positions in the opposite ends of the mid-region IIIof the envelope. The assemblies E, E being protected against oxidationby the vacuum in the envelope L, each tubular envelope end T is fusedand collapsed at I4 upon its inlead I3 behind the correspondingelectrode I2, as indicated in dot and dash lines in Fig. 2, thus notonly emmsssnss apart the discharge chamber I I with its rounded ends II,I], containing the electrodes l2, II,

as well as separate outer protective end chainbers 23, 23 enclosing theouter lead portions l3, ll outside the fused seals l4, l4. Shifting andlocating the assemblies E, E in this manner and making the fused sealsI, I4 is greatly facilitated by having the device L entirely detachedfrom the exhaust system at this time, so that it can be freelymanipulated by the glassworker.

It remains to complete the device L by conditioning it internally andcharging the discharge chamber in to provide the desired dischargeatmosphere therein for operation. For this purpose, the tube t may bereconnected or rescaled to the quartz tube s of the system S as shown at22 in Fig. 3-incidentally, of course, opening the tube t tothe-atmosphere and losing the vacuum in the device L-after introducingthe desired amount of mercury into the U bend of the tube t as shown inFig. 3. The device L is then again exhausted through the tube t, and apreliminary filling of starting gas at suitable pressure is preferablyintroduced, such as argon at min. After exhaust-processing the device Las now to be described in detail, including degasing its internalsurfaces and parts, withdrawing the temporary gas filling, and refillingwith pure starting gas such as argon at 2-0 mm. pressure, the device isagain tipped oil at 22, and the mercury at 2| is run into it by suitablemanipulation. The device L is-then finally tipped oil from the tube tclose to the discharge chamber III as hereinafter described.

As shown in Figs. 3 and 4, a number of identical devices L are connectedby corresponding tubes t to a common system S, to be concurrentlyexhaust-processed as just outlined. During the re-evacuation, the wholebatch of devices L are preferably enclosed and heated in athermo-insulative oven 30 to a temperature of some 1200 C., in order todegas their internal walls. The oven 30 may be equipped withlongitudinal electric heaters 3|, and may be arranged to slide up' anddown along guideways afforded by frame uprights 32, and suitablycounterweighted as indicated at 33. For entrance and exit of the devicesL and the tubes t to and from the oven 30, the oven has an opening 34in'its' bottom wall. When the oven is down around the devices L, itrests on a thermo-insulative floor 35 which closes the bottom opening34. As shown, the floor 35 is arranged to slide backward out of the way(or vice versa) along horizontal ways 36 carried by the frame uprights32, and has slots 31 to pass the tubes t during such movement. When theoven 30 is raised to its idle" position shown in Figs. 3 and 4, itsbottom opening 34 may be closed by a swinging bottom 38 fulcrumed at 39behind the rear uprights 32, and counterweighted as at 4| to keep itclosed except when pushed down and back behind the oven by the latter asit is lowered. Thus the oven 30 is always closed and at proper internaltemperature for baking the devices L. While the delvces L are in theoven 30, their outer leads l3, is are protected from oxidation by thesealed tube ends T, T, shown in Figs. 2, 3, and 4.

After exhausting the devicesv L while being baked in the oven 30, it isdesirable to pass current between the electrodes l2, l2 of each device Lto heat and degas them thoroughly by the "bombardment of the electricaldischarge, with- -ing of the envelope ends ll,

drawing the gas thus liberated through the tubes t and the exhaustsystem 8. To facilitate this, the oven 30 may be raised out of the wayto its position shown in Figs: 3 and 4. Capacitative couplings 4|, 4|may then be applied to each of the sealed tube ends T, T, such couplingsbeing' here shown in the form-of helical wire coils that can easily heslipped on these tube ends around and adjacent their ensealed inleadsl3, l3. One coupling ll of each device L being suitably grounded, as bya wire 42 connected to the machine frame at 43, the sparking end of ahighfrequency high-voltage Tesla coil device 44 (here illustrated in thecompact form commercially known as a Shelton coil") may be applied orbrought close to the other coupling ll of each device L. The A. C.discharge current thus passed between the electrodes l2, l2 should notbe so high or so long continued as to produce blacken- II, and need notbe sufficient to heat the electrodes visibly, but should be as high ascan be used without causing blackening. Ordinarily some 10 to 15 seconds(more or less) of such sparking is suflicient, according to the size ofthe electrodes l2, l2.

After the operation just described, the temporary gas filling and thegases liberated by the electrical bombardment are evacuated through thetubes t, and the final gas fillings are introduced through these tubest. This is followed by tipping off each device L at 22 again,introducing the mercury 24 for its charge I5 as above mentioned, andfinally sealing or tipping it off very close to envelope wall I, allaccording to usual capillary lamp practice. Finally, the exhaust sealtip is heated and fused just enough to allow it to be forced in by thepressure of the surrounding atmosphere, thus filling the usual exhausttip recess and producing a somewhat irregular conformation, that issuggested at 45 in Fig. 1. When the tube ends T, T are cut off beyondthe fused zones to afiord access to the outer lead portions l3, l9,device L is left with the end seals I 4, H as shown in Fig. 1.

A suitable operating and starting circuit for the lamp L is illustratedin Fig. l as comprising a step-up autotransformer A whose secondary isconnected across the leads l9, is, while its primary is connected acrossa supply line 50. One of the leads l3 includes a choke coil or ballast5|, while the other includes the switch-opening electromagnetic coil 53of a normally closed and selfclosing relay vacuum switch 54 in a shuntcircuit 55 connected across the leads i 9, I3. A control switch 56 isshown connected in one side of the supply line 50. When the controlswitch 58 is closed to energize the lamp supply circuit l3, IS, therelay switch 54 opens suddenly, producing a high-voltage surge acrossthe discharge gap between the lamp electrodes l2, l2 that initiatesdischarge between them.

In operation, the arc discharge takes place between the proximate innerends of the electrodes l2, l2, and the main body of the envelope l0around the electrode gap is heated directly by radiation and conductionfrom the arc stream, as well as by convection currents in the gas andvapor atmosphere of the lamp. The are also heats directly the activeinner ends of the electrodes from which it takes oil, and this heat ispartly transmitted back through the electrodes l2, I2 and their leadsl3, l3 to the walls of the end chambers II, II. Heat is also transmittedfrom the electrodes l2, l2 to the end chamber walls by radiation and bygaseous or vaporous conduction and convection. Thus the dischargemaintains the electrodes H, II at a temperature of ample electronemission which obviates serious sputtering of the electrodes, and hotenough throughout to keep the end chambers H, i I from anywhere fallingbelow a temperature corresponding to the desired mercury pressure. Atthe same time, the ver large radiation of energy from the ver hotelectrodes l2, I2 (which increases according to the fourth power oftheir temperature, measured on the Kelvin scale) prevents them fromattaining a temperature at which the metal would vaporize freely andseriously blacken the envelope In in a, short timeeven under a rise oflamp voltage above rated normal amounting to as much as to 20 per cent.The most favorable operating temperature for tungsten electrodes l2, I2is around 3000 K., with a leeway of several hundred degrees above orbelow this figure. This high temperature of the unactivated electrodesl2, IZ-considerably higher than would be practicable with activatedelectrodes, because of the vaporization of the usual activating oxidesat such high temperaturegreatly increases the heating of the endchambers II, II from the electrodes. In combination with the low thermalconduction of the silica of the end seals l4, ll, the low thermalconduction of the thin ribbon lead sections l8, I8 limits the loss ofheat along the leads l3, l3, and thus contributes to the adequateheating of the end chambers l I, I I and to maintaining the electrodesl2, H at a temperature of adequate thermionic emission. The rough orinterstitious surfaces of each electrode I2 (due to the V-groovesbetween its coil convolutions) greatly facilitate the starting of thearc discharge, making it possible to start at a much lower efiectivevoltage across the arc gap. The squat configuration of the electrode l2and its small mass and thermal capacity enable it to be heated up veryquickly when the discharge is started, so as to become adequatelyemissive from its arcing area before appreciable sputtering can occur.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of manufacturing electric discharge devices whichcomprises hermetically sealing portions of lead-in conductors carryingelectrodes at their inner ends into an envelope of vitreous materialwith the electrodes extending into the interior of the envelope, andalso hermetically enclosing the outer ends of said conductors invitreous material, evacuating the envelope and heating it to atemperature suflicient to oxidize the said outer ends of the conductorsin the absence of the enclosing vitreous material, permitting the deviceto cool, and then removing the vitreous material enclosing the said endsof said conductors.

2. The method of manufacturing electric discharge devices whichcomprises hermetically sealing portions of lead-in conductors carryingelectrodes at their inner ends into an envelope of vitreous materialwith the electrodes extending into the interior of the envelope, andalso hermetically enclosing the outer ends of said conductors invitreous material, evacuating the envelope and heating it to atemperature suflicient to oxidize the said outer ends of the conductorsin the absence of the enclosing vitreous material, applyingcapacitativecouplings to said envelope adjacent the lead-in conductorsand connectin said couplings to a source of alternating otential toinduce current flow between said electrodes and thereby electricallybombard and heat the electrodes, permitting the device to cool, and thenremoving the vitreous material enclosing the said ends of saidconductors.

EDWARD B. NOEL.

